edges are measured in pixels.. so if your style has edges set to 1px and you export an image 10,000px wide, the lines are going to appear tiny in the export.. if you want to export at that size with fatter lines, increase your profile settings in the style.. for instance, if your workspace is 1000px wide and you have edges set to 1px, you'll have to make your edges 10px to appear the same at 10,000px wide.
with sketchy styles, there's a problem if i understand correctly how they work.. the sketchy edges are raster images so if they scaled according to your export size, they'd look horrible/pixelated when blown up.. they'd look the same as if you exported a jpg at 999px wide then in an image editor, increased the size to 9999px wide..
i don't know if it's possible but you might have to create a custom sketchy style with really thick linework -or- really high resolution in order to export a giant JPG which inherits the sketchy style.. (like so thick that when viewing in the model space, it will look bad with way-too-big edges.. but when exported at 5x size, they look normal/good)